Since lithium ion secondary batteries have high energy densities, they are expected to be used for power sources for electric cars, hybrid vehicles, electric motorcycles, forklifts, and the like. In order to obtain an electric power source having a larger capacity, an assembled battery has been developed by connecting a plurality of batteries.
The lithium ion secondary battery includes a metallic outer can, a wound electrode group accommodated in the outer can, leads, and a metallic lid attached to an opening portion of the outer can. For example, the lid is welded to the opening portion of the outer can. A positive electrode current-collecting tab is provided at one end in a winding axis direction of the wound electrode group. A negative electrode current-collecting tab is provided at the other end thereof. The positive electrode current-collecting tab is connected with a positive electrode-lead. The negative electrode current-collecting tab is connected with a negative electrode-lead. The lid is equipped with a positive electrode terminal and a negative electrode terminal. These terminals are fixed to the lid by caulking. For example, a gasket becomes caught between these terminals and the lid, so that the terminals are insulated from the lid and the outer can. The positive and negative electrode-leads connected with the current-collecting tabs are respectively connected to the terminal of the positive electrode and the terminal of the negative electrode.
When the current-collecting tabs or the leads come into contact with the outer can of the battery, and in particular, in a case where it is an assembled battery, the outer can gets a high voltage, and there is the possibility of increasing danger of electric leak and electric shock to a person. Accordingly, a structure for insulating the outer can from the current-collecting tabs and the leads has been considered. However, in a case where vibration, shock, or the like is applied to the battery, there is the possibility that the current-collecting tabs and the leads may come into contact with the outer can. Alternatively, in a case where the leads are disconnected from the current-collecting tabs of the electrode group due to, e.g., vibration, shock, or the like, the leads may come into contact with the electrode group, and there is the possibility of causing short circuit.